The invention relates to yarn breakage detection circuits in knitting and other textile machines, and more particularly to circuitry within such detection arrangements for indicating the breakage visually and for stopping or otherwise altering a clutch drive which feeds the yarn into the knitting machine.
In known circuits of this type, the drive coil of a yarn-advancing clutch, illustratively a friction clutch, is normally maintained in a conductive state appropriate to permit the clutch to advance yarn into the machine. The conductive state of the drive coil is conventionally controlled by a transistor or other semiconductive device, whose control electrode is switched upon the occurence of a yarn breakage. A lamp or other suitable illumination device is connected to a reed switch, which is magnetically operated to excite the lamp simultaneously with the excitation of the control electrode of the coil-controlling transistor, i.e., upon the occurrence of a yarn breakage in the knitting machine.
The necessity, in such arrangements, of employing an active semiconductive control device for regulating the conductive state of the clutch drive coil leads not only to relatively high complication and expense of the detection circuitry, but also to relatively high susceptability of the circuit to noise disturbances and to changes of parameters of the circuit caused by changes in temperature and the like.